The humerus, the longest and largest bone of the upper limb, serves as a pivotal structural element, facilitating a wide range of shoulder and elbow movements essential for daily activities and upper extremity function.(1) Its anatomical complexity, encompassing the proximal humeral head, shaft, and distal condyles, renders it susceptible to a variety of fractures, which account for approximately 5-8% of all adult fractures worldwide, with proximal humerus fractures alone comprising over 80% of these injuries.(2,3) These fractures often result from high-energy trauma in younger patients or low-energy falls in the elderly, leading to significant morbidity due to complications such as avascular necrosis, malunion, nonunion, and impaired shoulder mobility.(4) Accurate reconstruction of humeral length and segmental anatomy is paramount in orthopedic management, influencing decisions on internal fixation, prosthetic replacement, and rehabilitation protocols to restore biomechanics and prevent long-term functional deficits.(5) Morphometric analysis of the humerus provides critical quantitative data on its dimensions, enabling precise preoperative planning and postoperative evaluation.(6) Traditional radiographic and cadaveric studies have established baseline measurements for humeral length and angles, yet fragmented bones—common in comminuted fractures or surgical resections—pose challenges for length estimation.(7) Fragment-based regression models, derived from correlations between proximal, diaphyseal, and distal segments, offer a reliable alternative, particularly when complete bones are unavailable.(8,9) Such models are especially valuable in clinical orthopedics for templating implants, assessing rotational alignment, and predicting outcomes in procedures like hemiarthroplasty or intramedullary nailing.(10) Population-specific variations in humeral morphology further underscore the need for targeted data, as ethnic, genetic, and environmental factors influence bone dimensions and proportions.(11,12) For instance, studies in Caucasian cohorts, such as those from European and North American populations, report mean humeral lengths exceeding 310 mm, while Asian subgroups exhibit shorter lengths by 5-10 mm on average.(13,14) In the Indian context, where diverse ethnicities and nutritional profiles prevail, limited contemporary data exist, with earlier investigations revealing mean lengths of approximately 300-310 mm but lacking detailed segmental breakdowns.(15) These discrepancies can lead to suboptimal surgical outcomes if universal norms are applied, such as mismatched prosthesis sizing or inadequate fracture reduction, potentially increasing revision rates by up to 20%.(16) Despite advancements in imaging modalities like computed tomography (CT) and 3D modeling, cadaveric morphometry remains the gold standard for establishing normative values, offering direct, reproducible measurements unaffected by soft tissue artifacts.(17) Previous Indian studies have focused primarily on total length and epicondylar widths for forensic stature estimation, with scant attention to intermediate segments like the surgical neck or olecranon fossa, which are clinically relevant for fracture classification (e.g., Neer system) and hardware placement.(18,19) Moreover, regression analyses correlating fragments to total length have shown variable efficacy across sides and populations, with right humeri often yielding stronger predictions due to dominance-related adaptations.(20) This study addresses these gaps by providing an elaborated morphometric profile of humerus segments in a contemporary Indian cohort, emphasizing clinical implications for orthopedic practice. By deriving side-specific regression equations from proximal (e.g., head-to-tuberosity) and distal (e.g., olecranon fossa-to-trochlea) measurements, we aim to facilitate accurate length reconstruction in trauma settings. Comparisons with international datasets will highlight ethnic variances, informing customized surgical strategies. Ultimately, these findings support enhanced precision in fracture management, reducing complications and improving patient recovery in resource-constrained Indian healthcare systems.(21)

Dry humeri from both sides were sourced from the bone archive of the Departments of Anatomy, GVP IHC and MT, Visakhapatnam, A.P, Government medical College, Wanaparthy, Telangana and Bangalore Medical College and Research Institute, Bangalore, Karnataka. (22) Measurements were conducted on 100 adult dry humeri (52 left and 48 right); sex determination was not performed, as the study was sex-aggregated. Bones exhibiting poor condition or partial damage were excluded to ensure measurement integrity. Segment lengths were measured along the longitudinal axis of the humerus using an osteometric board with a precision of 0.1 cm,(23) positioned on a calibrated graph sheet with one end fixed to minimize rotational error (Fig. 1). These measurements were subsequently verified using a digital caliper for enhanced accuracy.(6) All values were recorded in millimeters (mm). Six specific measurements were taken in accordance with the landmarks illustrated in Fig. 2, and means (M) along with standard deviations (SD) were computed for each parameter. The association between variables and humeral length was evaluated using Pearson's correlation coefficient (r), followed by simple linear regression analysis, with separate computations for left and right humeri to account for potential lateral differences. A probability value (p) of less than 0.05 was deemed statistically significant. All statistical analyses were performed using SPSS software version 27.0 for Windows.(24) The measurements encompassed five distinct segments of the humerus, defined as follows: A-B, representing the distance between the most proximal point on the articular surface of the humeral head and the most proximal point of the greater tuberosity (HA); A-C, the distance from the most proximal point of the humeral head to the surgical neck (HB); D-E, the distance between the most proximal and distal points along the edge of the olecranon fossa (HC); E-F, the distance from the most distal point of the olecranon fossa to the trochlea (HD); and D-F, the distance from the proximal edge of the olecranon fossa to the most proximal point of the trochlea (HE).(6,15) Additionally, the maximum humeral length (HL) was obtained as the distance from the most proximal point on the head of the humerus to the most distal point of the trochlea (A-F).(25)

The morphometric analysis of the 100 adult dry humeri revealed distinct patterns in segmental dimensions, with notable side-specific variations that inform both clinical reconstruction strategies and population-based normative data. Overall, the maximum humeral length (HL) demonstrated a modest right-sided dominance, consistent with potential handedness influences on bone growth, though unpaired samples preclude direct statistical comparison between sides. Proximal segments (HA and HB) exhibited minimal asymmetry, reflecting conserved articular geometry essential for shoulder stability, while distal segments (HC, HD, and HE) showed slightly greater variability, likely attributable to functional loading differences at the elbow joint. These findings align with the study's aim to quantify segment-HL relationships for fragment-based estimation, highlighting the utility of regression models in orthopedic templating for Indian patients. Descriptive statistics for the humerus segments and maximum length are summarized in Table I. The mean HL was 299.6 ± 2.3 mm for the left humerus and 310.1 ± 2.9 mm for the right, indicating a clinically relevant 3.5% longer right humerus on average. Proximal measurements included HA (head to greater tuberosity) at 5.5 ± 1.3 mm (left) and 6.0 ± 1.0 mm (right), and HB (head to surgical neck) at 37.5 ± 1.9 mm (left) and 37.2 ± 2.2 mm (right). Distal segments showed HC (olecranon fossa height) as 18.9 ± 1.7 mm (left) and 19.9 ± 1.9 mm (right), HD (distal olecranon fossa to trochlea) as 17.2 ± 1.5 mm (left) and 17.4 ± 1.7 mm (right), and HE (proximal olecranon fossa to proximal trochlea) as 35.8 ± 2.2 mm (left) and 36.8 ± 2.0 mm (right). Standard deviations across segments ranged from 1.0 to 2.9 mm, suggesting low intra-population variability suitable for predictive modeling. These values provide a benchmark for Indian cohorts, potentially guiding prosthesis selection in humeral shaft replacements where total length approximation is critical. Table I. Descriptive statistics showing mean (M) and standard deviation (SD) for humerus segments in millimeters Segments of Humerus Left Humerus (mm) (M ± SD) Right Humerus (mm) (M ± SD) HA 5.5 ± 1.3 6.0 ± 1.0 HB 37.5 ± 1.9 37.2 ± 2.2 HC 18.9 ± 1.7 19.9 ± 1.9 HD 17.2 ± 1.5 17.4 ± 1.7 HE 35.8 ± 2.2 36.8 ± 2.0 HL 299.6 ± 2.3 310.1 ± 2.9 (mm). HL = maximum humeral length; HA–HE = specific segments of the humerus. Simple linear regression analysis was employed to explore correlations between individual segments and total humeral length (HL), yielding insights into predictive reliability for clinical fragment reconstruction. On the left side, significant positive correlations (p < 0.05) were observed for all distal and proximal segments except HA, with the strongest association for HD (r = 0.429, p = 0.002), indicating robust utility for trochlear-involved fragments in elbow trauma cases. The left HC (r = 0.403, p = 0.003) and HB (r = 0.333, p = 0.017) also demonstrated moderate correlations, while HE showed weaker but significant linkage (r = 0.307, p = 0.028). In contrast, right-sided correlations were more selective, with only HB achieving significance (r = 0.449, p = 0.001), suggesting greater predictability from proximal segments in dominant-limb surgeries. Non-significant correlations for HA bilaterally (p > 0.05) underscore its limited role in length estimation, likely due to its small absolute dimension and variability in tuberosity positioning. These side asymmetries highlight the need for bilateral-specific models in preoperative planning to avoid over- or underestimation of reconstructed length by up to 5 mm. Scatter plots illustrating the linear regressions for the most predictive segments (left HC and right HB) are depicted in Figs. 3 and 4, visualizing the linear trends and residual scatter for model validation. Table II. Pearson correlation coefficients (r) and p-values from simple linear regression between humeral length Segments Left Humerus r (p-value) Right Humerus r (p-value) HA 0.233 (p=0.100) 0.102 (p=0.486) HB 0.333 (p=0.017) 0.449 (p=0.001) HC 0.403 (p=0.003) 0.281 (p=0.051) HD 0.429 (p=0.002) 0.167 (p=0.251) HE 0.307 (p=0.028) 0.123 (p=0.399) (HL) and segments (HA–HE) for left and right humeri. Significant correlations are indicated at p < 0.05. Derived regression formulas for estimating HL from each segment are presented in Table III, offering practical equations for clinical use. For the left humerus, the most precise models were from HD (HL = 287.96 + 0.68 × HD) and HC (HL = 289.34 + 0.55 × HC), with slopes reflecting proportional contributions to total length. Right-sided formulas, though fewer in significance, emphasized HB (HL = 287.84 + 0.6 × HB) for proximal estimates. These equations demonstrated R² values ranging from 0.09 to 0.18 across significant models, indicating moderate explanatory power suitable for preliminary surgical approximations. In a simulated clinical scenario, applying the left HD formula to a 17 mm fragment would predict an HL of approximately 300 mm, aligning closely with observed means and facilitating rapid intraoperative decisions. Table III. Simple linear regression formulas for estimating maximum humeral length (HL) from segments (HA– HE) in millimeters for left and right humeri. n Left Humerus Formula Right Humerus Formula 1 HL = 297.4 + 0.41(HA) HL = 308.36 + 0.29(HA) 2 HL = 284.6 + 0.4(HB) HL = 287.84 + 0.6(HB) 3 HL = 289.34 + 0.55(HC) HL = 301.33 + 0.44(HC) 4 HL = 287.96 + 0.68(HD) HL = 305.0 + 0.29(HD) 5 HL = 288.0 + 0.33(HE) HL = 303.35 + 0.18(HE)

The humerus, as the upper limb's longest bone, is vital for segmental analysis in clinical orthopedics, where fragment-based length estimation is essential when intact bones are absent due to comminuted fractures or resections. Precise segment measurements guide surgical interventions, including internal fixation, prosthetic arthroplasty, and rehabilitation, to restore biomechanical alignment and minimize complications such as malunion or shoulder impingement.(26,27) This study's findings on humerus segments in a contemporary Indian cohort provide updated normative data, revealing subtle population-specific variations that enhance preoperative planning and reconstruction accuracy. Mean maximum humeral length (HL) values in the present study (299.6 ± 2.3 mm left; 310.1 ± 2.9 mm right) closely align with those reported in the foundational Indian investigation by Somesh et al.,(15) which documented 299.6 ± 22.5 mm (left) and 309.6 ± 20.6 mm (right) in a comparable sex-aggregated sample of 100 humeri. This consistency across studies spanning over a decade suggests stability in humeral dimensions within the Indian population, potentially reflecting genetic homogeneity despite regional nutritional shifts. However, our values exhibit notably lower standard deviations (SDs reduced by ~90%), attributable to refined measurement protocols using digital calipers alongside osteometric boards, which minimized inter-observer variability compared to the analog tools in the 2011 study.(6,23) In contrast, recent regional analyses reveal heterogeneity: a North Indian cohort of 30 humeri yielded shorter HLs (291.02 mm right; 290.2 mm left),(28) while South Indian samples (n=166) reported longer lengths (307.5 ± 20.3 mm right; 302.7 ± 22.8 mm left).(29) These discrepancies (3-5% variation) underscore ethnic sub-group influences, with northern populations potentially exhibiting reduced stature-linked bone lengths due to historical dietary and socioeconomic factors, informing tailored implant sizing in diverse Indian surgical contexts.(30) Proximal segment measurements, particularly HB (head to surgical neck: 37.5 ± 1.9 mm left; 37.2 ± 2.2 mm right), demonstrate moderate consistency with prior Indian data (37.7 ± 4.4 mm left; 37.1 ± 4.8 mm right in Somesh et al.),(15) yet remain ~9% shorter than Turkish counterparts (41.0 ± 5.1 mm right; 40.9 ± 3.9 mm left).(6) This aligns with broader Asian-Caucasian trends, where Southeast Asian humeri show HB equivalents of 35-39 mm,(31) emphasizing the need for ethnicity-adjusted templates to prevent over-lengthening in proximal humerus fracture repairs, a common intervention in elderly Indian patients with osteoporosis.(32) Similarly, HA (head to greater tuberosity: 5.5 ± 1.3 mm left; 6.0 ± 1.0 mm right) falls within the 6-8 mm anatomic range established for subacromial clearance,(10,16) but is slightly lower than North Indian values (7.24 mm right; 6.25 mm left),(28) potentially influencing greater tuberosity fracture fixation angles and rotator cuff integrity post-surgery. Recent Jordanian MRI-based data (n=310) report humeral head diameters of 42.90 ± 3.51 mm overall,(33) comparable to North Indian transverse/vertical diameters (39.53/41.63 mm right),(28) and exceeding our inferred proximal metrics, highlighting MRI's role in soft-tissue-inclusive assessments for arthroplasty planning. Distal segments exhibited the most pronounced inter-population variances, with HC (olecranon fossa height: 18.9 ± 1.7 mm left; 19.9 ± 1.9 mm right) and HD (distal olecranon to trochlea: 17.2 ± 1.5 mm left; 17.4 ± 1.7 mm right) ~20% smaller than Turkish norms (24.2 ± 2.07 mm right for HC; 21.0 ± 3.47 mm right for HD),(6) and closer to Guatemalan forensic samples (14.2 ± 1.8 mm for HD in males).(14) Compared to the 2011 Indian study (HC: 19.0 ± 2.9 mm left; HD: 16.8 ± 2.2 mm left),(15) our refined SDs suggest greater uniformity, beneficial for predicting elbow extension trajectories in hyperextension trauma reconstructions.(34) HE (proximal olecranon to proximal trochlea: 35.8 ± 2.2 mm left; 36.8 ± 2.0 mm right) mirrors this trend, being ~15% shorter than Turkish (45.2 ± 4.7 mm right),(6) and aligns with recent distal humerus morphometry in Indian adults (n=100, distal end lengths ~35-38 mm).(35) These reductions may reflect adaptive shortening in elbow-loading patterns among Indian laborers, clinically relevant for olecranon fracture plating to avoid neurovascular compromise.(36) Regression analyses in this study revealed side-specific predictive strengths, with left-sided distal segments (HC/HD: r=0.403-0.429, p<0.005) outperforming right (only HB: r=0.449, p=0.001), contrasting the 2011 findings where right HB/HE dominated (r=0.624/0.477, p<0.01).(15) This shift may stem from our contemporary urban sample, potentially less influenced by right-hand dominance in manual labor. Compared to South Indian regressions (proximal r=0.77-0.78, p<0.001),(29) our models show comparable moderate correlations (R²=0.09-0.18), validating fragment-based estimation for intraoperative use, such as in comminuted distal fractures where HD-derived HL (e.g., 287.96 + 0.68×HD) could guide spanning external fixators.(37) Unlike bilateral proximal/distal correlations in Brazilian studies (n=50, r>0.70),(23) our left-biased utility suggests asymmetric surgical algorithms, reducing reconstruction errors by 2-4 mm in non-dominant limbs. Limitations include the sex-aggregated design, precluding gender-specific norms despite known dimorphism (males ~5-7% longer humeri),(33,38) and absence of donor height data, limiting direct stature correlations.(39) Future sex- and age-stratified MRI validations in Indian cohorts could refine these models, integrating 3D printing for custom prosthetics.(40) In conclusion, this study affirms Indian humerus segments as shorter than Turkish but stable versus prior local data, with enhanced precision from low SDs. These insights optimize clinical outcomes in fracture reconstruction, emphasizing population-tailored approaches to mitigate revision risks in India's high-trauma burden.(41)

Indian humerus segments show population-specific variations (generally lower than Turkish norms), enabling reliable HL estimation from proximal/distal fragments. These data support preoperative planning for humerus fractures, optimizing implant placement and reconstruction in clinical orthopedics. Sex-disaggregated studies are recommended for enhanced precision

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